1. Field of the Invention
The present invention relates to a method for knock detection in an internal combustion engine and, more particularly, to a process of detecting knock in an internal combustion engine, in which the presence of knock is established, when the detected, if necessary amplified, knock sensor signal exceeds a reference level, which changes according to the noise or sound level of the operating internal combustion engine.
2. Description of the Related Art
Combustion events, which lead to knock, can occur in the cylinders of an internal combustion engine, during its operation. These combustion events, which can lead to destruction of the internal combustion engine, must be reliably detected, so that measures to prevent further knocking can be rapidly performed. Usually sensors are employed for knock detection, which are associated with the cylinders of the internal combustion engine and which supply a signal, which depends on the noise or sound level of the internal combustion engine and on the knock sounds occurring in it.
The output signals of the knock sensors are usually evaluated in a control unit of the internal combustion engine, which controls the ignition and/or injection according to the knock detection. The special problem with knock detection is that the knock sounds must be distinguished from a variety of other sounds, especially the basic sounds of internal combustion engine operation. It is thus known to perform a special evaluation process for knock detection. The basis for the usual knock detection is the formation of a reference level of the basic sounds from the internal combustion engine when it is operating without knocking or knock events. This reference level is determined from the output signals of the knock sensors for the individual cylinders by the control unit. This determination can occur in a cylinder-specific manner or as an average over the cylinders. The reference level is calculated during operation continually so that the actual conditions of the internal combustion engine are continually represented in it. A formula (1) for computation of the reference level is, for example, given by:rkr(new)=rkr(old)·[(KRFTP−1)/KRFTP]+ikr/KRFPT  (1)                wherein rkr(new) represents the new reference level;        rkr (old) represents the old reference level;        KRFTP represents a factor for tracking the reference level, a typical value for KRFTP being 16 in knock free operation; and        ikr represents the integrated value of the actual combustion events, usually of the amplified knock signal in a predetermined range.        
During rapid sound changes, for example because of rapid load or rotation speed changes, the tracking factor KRFTP is less than 16. In load or rotation speed changes the sound changes in all cylinders are similar. The reference level tracking occurs also in knocking operation by the above-mentioned formula. When no knocking combustion events are occurring, the actual integrated value is computed as described above. During knocking combustion the actual integrated value is not completely calculated, but is corrected prior to calculating. The ratio of the actual integrated value ikr to the reference level rkr is formed for actual knock detection. When this ratio exceeds a predetermined threshold value, it is established that knock is occurring. A device for knock detection using the above-described procedure is described, for example, in German Patent Document DE-OS 43 339 65 and/or U.S. Pat. No. 5,743,233, which belong to the same patent family.